This invention relates in general to a color proofing apparatus and method of manufacture and more particularly to alignment of a bearing hub in a print engine chassis.
Pre-press color proofing is a procedure used by the printing industry for creating representative images of printed material. This procedure avoids the high cost and time required to produce printing plates and also avoids setting-up a high-speed, high-volume printing press to produce a representative sample of an intended image for proofing. Otherwise, in the absence of pre-press proofing, a production run may require several corrections and must be reproduced several times to satisfy customer requirements. This results in lost profits. By utilizing pre-press color proofing, time and money are saved.
A laser thermal printer having half-tone color proofing capabilities is disclosed in commonly assigned U.S. Pat. No. 5,268,708 titled xe2x80x9cLaser Thermal Printer With An Automatic Material Supplyxe2x80x9d issued Dec. 7, 1993 in the name of R. Jack Harshbarger, et al. The Harshbarger, et al. device is capable of forming an image on a sheet of thermal print media by transferring dye from a roll of dye donor material to the thermal print media. This is achieved by applying thermal energy to the dye donor material to form the image on the thermal print media. This apparatus generally comprises a material supply assembly, a lathe bed scanning subsystem (which includes a lathe bed scanning frame, a translation drive, a translation stage member, a laser printhead, and a rotatable vacuum imaging drum), and exit transports for thermal print media and dye donor material.
The operation of the Harshbarger, et al. apparatus comprises metering a length of the thermal print media (in roll form) from a material supply assembly. The thermal print media is then measured and cut into sheet form of the required length, transported to the vacuum imaging drum, registered, and then wrapped around and secured onto the vacuum imaging drum. Next, a length of dye donor roll material is also metered out of the material supply assembly, measured and cut into sheet form of the required length. The cut sheet of dye donor roll material is then transported to and wrapped around the vacuum imaging drum, such that it is superposed in registration with the thermal print media, which at this point has already been secured to the vacuum imaging drum. The drum is rotated past the printhead and the translation drive traverses the printhead and translation stage member axially along the rotating vacuum imaging drum in coordinated motion with the rotating vacuum imaging drum. These movements combine to produce the image on the thermal print media. After the intended image has been written on the thermal print media, the dye donor material is removed from the vacuum imaging drum without disturbing the thermal print media. Additional dye donor materials are sequentially superposed with the thermal print media on the vacuum imaging drum, then imaged onto the thermal print media as previously mentioned, until the intended full-color image is completed.
Although the printer disclosed in the Harshbarger, et al. patent performs well, there is a long-felt need to reduce manufacturing costs for this type of printer and for similar types of imaging apparatus. With respect to the lathe bed scanning frame disclosed in the Harshbarger, et al. patent, the machined casting used as the frame represents significant cost relative to the overall cost of the printer. Cost factors include the design and fabrication of the molds, the casting operation, and subsequent machining needed in order to achieve the precision necessary for a lathe bed scanning engine used in a printer of this type. Castings can be complex to model, making it difficult to use tools such as finite element analysis to predict the suitability of a design. Moreover, due to shrinkage, porosity, and other manufacturing anomalies, careful mold maintenance may be required in order to obtain uniform results when casting multiple frames. In the assembly operation, each frame casting must be individually assessed for its suitability to manufacturing standards and must be individually machined. Further, castings also exhibit frequency response behavior due to resonant frequencies, which are difficult to analyze or predict. For this reason, the task of identifying and reducing vibration effects can require considerable work and experimentation. Additionally, the overall amount of time required between completion of a design and delivery of a prototype casting can be several weeks or months.
The combined weight of the imaging drum, motor and encoder components, and printhead translation assembly components, plus the inertial forces applied when starting and stopping the drum require a frame having substantial structural strength. For this reason, a sheet metal frame would not be considered to provide a solution. Alternative methods used for frame fabrication have been tried, with some success. For example, welded frame structures have been used. However, these welded structures can require significant expense in manufacture. Welded structures can be adversely affected by stress induced by the welding process, causing warping.
Other alternatives to metal castings have been used by manufacturers of machine tools. In particular, castable polymers, manufactured under a number of trade names, have been employed to provide support structures that are equivalent to castings for apparatus such as machine tool beds and optical tables. These castable polymers also provide improved performance when compared with castings, with respect to expansion and contraction due to heat and with respect to vibration damping.
Castable polymers have been employed to provide substitute structures for metal castings and weldments. One example is disclosed in U.S. Pat. No. 5,415,610 (Schutz et al.) which discloses a frame for machine tools using castable concrete to form a single casting of a bed and a vertical wall for a machine tool. U.S. Pat. No. 5,678,291 (Braun) and 5,110,283 (Bluml et al.) are just two of a number of examples in which castable polymer concrete is used as a machine tool bed or for mounting guide rails in machining environments. Castable polymers are also used in the machine tool environment for damping mechanisms, as is disclosed in U.S. Pat. No. 5,765,818 (Sabatino et al.)
Castable polymers provide a number of advantages, including the ability to mount support components of the chassis directly in the castable material when it is still soft. Various types of fasteners, tubing, or other components can be cast in place, or can even be inserted into the castable polymer before it hardens. Of particular difficulty, however, is the precision placement of support components within the castable polymer material. In order to precisely position a component within such a material used as filler in a chassis, it is necessary to employ some type of temporary fixture or jig to hold the component in place temporarily during the hardening process. This positioning problem is compounded when it is necessary to mount two or more support components that must be axially aligned with respect to each other, such as the bearing hubs that support each end of an imaging drum.
Conventional alternatives for mounting right and left bearing hubs in precise placement with respect to each other include machining. After casting, machining operations such as boring and line honing or even line boring can be employed. As disclosed in U.S. Pat. Nos. 4,451,186 (Payne), 4,979,850 (Dompe), and 4,693,642 (Mair et al.), line boring machinery and techniques are employed for engine blocks and other precision castings. Line boring equipment, as described in these patents, solves the difficult problem of boring holes on opposite side walls of a chassis or engine, where axial alignment must be within very tight tolerances. However, line boring equipment is very expensive and requires building of specialized jigs and supports.
Components can be mounted in a castable concrete polymer that holds them in position, as is disclosed for attachment elements in a band saw in U.S. Pat. No. 4,557,171 (Stolzer). By the nature of castable fillers, precision positioning can be effected. For example, U.S. Pat. No. 4,425,171 (Oosaka et al.) discloses use of a substantially non-fluid bonding component (for example, epoxies) for precision positioning. The methods and materials disclosed in the Oosaka patent are intended primarily for service with lightweight optical components. These can be positioned by hand, as noted in the Oosaka et al. patent disclosure. However, such manual positioning methods cannot be suitably applied for mounting bearing hubs in precise alignment, since the bearing hubs have considerable mass relative to the devices noted in the Oosaka et al. patent. Moreover, bearing hubs require a jig or fixture so that when in position, these components are axially aligned. On a larger scale, U.S. Pat. No. 4,593,587 (Nenadal) discloses mounting of a way block in precise position on the bed of a machine tool using a castable filler material and employing a temporary fixture to secure this component in place during hardening. However, neither the Oosaka et al. nor the Nenadal patents address the more complex problem of positioning multiple components having axial alignment.
There has been a long-felt need to reduce the cost and complexity of printer fabrication without compromising the structural strength required for the lathe bed scanning assembly. While use of castable polymers provides an alternative to the use of conventional castings or weldments, the problem of precision positioning of support components when using castable materials requires cost-effective and reliable solutions.
It is an object of the present invention to provide an apparatus and a method for a bearing hub alignment in a print engine chassis, where the chassis uses side walls comprising a castable material.
According to one aspect of the present invention a method of aligning a bearing hub in a print engine chassis supporting an imaging drum provides a right wall positioned near a first end of the imaging drum and has a first cavity near the first end of the imaging drum. The present invention also provides a left wall positioned near a second end of the imaging drum, the left wall substantially parallel to said right wall, wherein the left wall has a second cavity near the second end of the imaging drum. A self-hardening filler material is poured into the first and second cavities. A right bearing hub is positioned for the imaging drum into the filler material within the first cavity prior to hardening of the filler material. A left bearing hub is positioned for the imaging drum into the filler material within the second cavity prior to hardening of the filler material. Alignment of the left bearing hub with the right bearing hub is needed.
According to one embodiment of the present invention, a precision mandrel is employed to axially align the bearing hubs, the mandrel itself supported on a fixture. A jackscrew positions the bearing hub on the mandrel before casting with filler material to allow removal of the mandrel when the filler material hardens.
A feature of the present invention is the provision of a print engine chassis comprising a filler material, wherein split bearing hubs are used to support bearings for the imaging drum, the bearing hubs themselves rigidly set in castable filler material.
An advantage of the present invention is that it eliminates the need for precision line boring machining for the purpose of creating axially aligned bores in facing chassis walls. Instead, modular split bores are set in castable filler material during chassis fabrication.
Yet another advantage of the present invention is that parts can be added to a chassis during assembly, at the time the castable polymer filling is applied. This saves cost over machining and allows changes to be easily incorporated into the design.
The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below.